Variable capacity hydrostatic axial piston machine

ABSTRACT

The invention relates to a variable capacity hydrostatic axial piston machine having a drive shaft which has a drive flange having an end face oriented towards displacement pistons in which end face spherical shells for holding substantially spherical piston heads are formed. The calotte of the spherical shells in this case go beyond the semisphere and each have a circular opening with a smaller diameter than the spherical shell diameter. The spherical calotte of the piston heads have a recess having a smaller diameter than that of the circular opening of the spherical shells so that at the vertex of the piston a spherical section making up less than the semisphere and, spaced apart from the latter by the recess a retaining collar having a larger diameter than the circular opening of the spherical shells are formed. A transverse groove is formed in the circular openings of the spherical shells in such a way that the piston head with the retaining collar can be threaded into the spherical shell through the transverse groove and is retained there in the working position of the piston.

BACKGROUND OF THE INVENTION

The invention relates to a variable capacity hydrostatic axial piston machine according to the features of claim 1.

Variable capacity hydrostatic machines which, for example, are used as hydraulic motors, have a cylinder drum which is mounted such that it can rotate about its central longitudinal axis and has cylinder bores distributed on its circumference, in which pistons can be displaced. The cylinder drum is mounted in the housing of the axial piston machine such that it can pivot about a pivot axis running transversely with respect to its axis of rotation, so that the central longitudinal axis of the cylinder drum forms an adjustable angle with the axis of the drive shaft. The pistons are supported in an articulated manner on the drive flange of the drive shaft at the adjustable angle. The spherical piston heads are in this case pivotably mounted in spherical shells, which are formed in the drive flange or in piston shoes fitted there. In order to be able to insert the spherical heads of the pistons into the spherical shells and to hold them axially there during the operation of the machine, they are generally retained by a retaining device which engages behind the spherical heads, for example by a perforated plate screwed on. An axial piston machine of this type is known, for example from EP 1 251 271 A2.

Also known are spherical joint connections having a spherical shell which encloses an angle which is greater than 180°. In order to be able to insert the spherical head, the latter has lateral flats or recesses, so that it can be inserted at an angle deviating from the working position and is held in the working position by the spherical shell. Spherical joints of this type are described, for example, in DE-OS 2 307 641.

It is an object of the invention to specify an axial piston machine of the type described at the beginning having improved spherical guidance of the pistons in the drive flange.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved 10 with a variable capacity hydrostatic axial piston machine which has a drive shaft with a drive flange having an end face oriented towards displacement pistons, in which end face spherical shells for holding substantially spherical piston heads are formed. The calotte of the spherical shells in this case go beyond the semisphere and have a circular opening with a smaller diameter than the spherical shell diameter. The spherical calotte of the piston heads have a recess having a smaller diameter than that of the circular opening of the spherical shells so that at the vertex of the piston a spherical section making up less than the semisphere and, spaced apart from the latter by the recess a retaining collar having a larger diameter than the circular opening of the spherical shell are formed. A transverse groove is formed in the circular opening of the spherical shell in such a way that the piston head with the retaining collar can be threaded into the spherical shell through the transverse groove and is retained there in the working position of the piston.

With the invention, for example a piston shoe can be dispensed with and overall space for a larger domed sphere can be obtained, at the same time a smaller total overall length being achieved. The larger domed sphere in this case permits a high level of balance of the hydrostatic load from the piston force, so that only a small part of the piston force has to be transmitted mechanically via the frictional contact.

The retaining collar preferably forms a spherical layer, which begins approximately in the middle of the spherical dome of the piston heads and extends approximately from the middle of the spherical dome beyond the latter by about ⅛ to ¼, preferably about ⅙, of the sphere diameter, which means that the height of this spherical layer is between ⅛ and ¼ of the sphere diameter, preferably ⅙ of the sphere diameter. Therefore, the part of the solid sphere on the piston side is eliminated. The piston rod can adjoin the retaining collar directly.

The recess is preferably rotationally symmetrical in relation he piston longitudinal axis. Therefore, economical manufacturing by turning is possible. The same advantage results during the production of the transverse grooves if they are formed rotationally symmetrically in relation to the axis of the drive shaft and form a circular ring around the latter.

The particular advantage of the invention resides in the fact that in order to thread them into the spherical shells the pistons can be set at an angle to the end face of the drive flange which is smaller than the smallest such angle occurring during the operation of the axial piston pump.

Therefore, the threading of the pistons can be carried out in blique position which does not occur during the operation of the machine so that the piston heads are retained securely in the spherical shells. The difference between the mounting and operating positions of the piston may be enlarged further by mounting grooves being provided in the end face of the drive flange which make threading possible at a minimum angle between the end face of the drive flange and the piston longitudinal axis.

The pistons preferably have a bore in the longitudinal direction through which hydraulic pressure is led from the cylinder chamber to the spherical dome of the piston head for the purpose of balancing the hydrostatic load on the mounting. This load relief is optimized by the fact that, firstly, in order to limit the hydrostatic balancing force, a circumferential groove is formed in the spherical section of the piston head and is surrounded on the outside by an annular spherical layer as a sealing surface, and secondly, a spiral groove is formed in the spherical section of the piston head from the bore as far as the circumferential groove.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention emerge from the following figure description.

In the drawing:

FIG. 1 shows an exemplary embodiment of the invention with the mounting position of the piston;

FIG. 2 shows the exemplary embodiment from FIG. 1 with the piston mounted;

FIG. 3 shows an exemplary embodiment of the piston;

FIG. 4 shows the piston from FIG. 3 in a perspective view; and

FIG. 5 shows the mounting of the piston in a sectional illustration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an exemplary embodiment of the invention is shown in the state in which the piston is being mounted and threaded into the associated spherical shell of the drive flange. The drive shaft 1 of the variable capacity axial piston machine has a drive flange 2, on whose end face 3 the pistons 4 are pivotably mounted. For this purpose spherical shells 5 are formed in the end face 3 of the drive flange 2 and accommodate the spherical heads 6 of the displacement pistons 4. The spherical shells 5 go beyond the semisphere. They comprise an angle which is greater than 180° and open towards the pistons with a circular opening 7 which is smaller than the spherical shell diameter.

The mounting of the piston is made possible by the fact that a transverse groove 11 passing through the circular opening 7 is formed and in the example illustrated, as a circumferential groove forms a circular ring around the longitudinal axis of the drive shaft. The specially designed head 6 having the retaining collar 10 is pushed into the spherical shell obliquely in the axial direction through this transverse groove 11. The retaining collar 10 and the groove dimensions are configured in such a way that the mounting of the pistons is possible only with the illustrated highly oblique position of the piston axis in relation to the shaft axis. The angle between the end face 3 of the drive flange 2 and the piston axis can be kept particularly small by the fact that mounting grooves 12 running radially from the shaft axis to the spherical shells 5 are provided in the end face 3 of the drive flange 2, so that an extreme oblique position can be achieved which deviates considerably from the working position of the pistons, in which only smaller oblique positions occur, equivalent to a considerably larger angle between the piston axis and the end face 3.

FIG. 2 corresponds to the illustration of FIG. 1 and shows the piston 4 in the mounted position with the spherical head 6 pushed into the spherical shell 5 and an orientation of the pistons corresponding to their working position. The circumferential transverse groove 11 and the mounting grooves 12 are formed as in FIG. 1. Alternatively, the construction can also be designed such that the mounting grooves 12 run outwards, for example, the pistons 4 assuming a position during the mounting which is not oriented obliquely towards the shaft axis but outwards, obliquely away from the shaft axis.

In FIGS. 3 and 4, the piston 4 with its head 6 is illustrated detail. The piston 4 extends along the piston longitudinal axis 19. The head 6 is basically spherical with a diameter 18 in order to form a spherical joint with the spherical shells in the drive flange. The center of the sphere of the piston head 6 and its vertex 13 lie on the piston longitudinal axis 19. The sphere of the head 6 is in this case not formed as a solid body. To a certain extent, it is reduced to a spherical section 9 at the vertex 13 of the piston 4 and to the retaining collar 10. In the example illustrated the spherical section at the vertex 13 has, in the direction of the piston longitudinal axis, a height of about ⅕ to ¼ of the sphere diameter. A recess 8 is provided between spherical section 9 and retaining collar 10. This recess 8 has a diameter which is smaller than the diameter of the circular opening 7 of the spherical shell and reaches approximately as far as the central plane of the sphere. The retaining collar 10 forms a spherical layer and extends from approximately the central plane of the sphere in the direction of the adjacent piston rod 21 with a spherical layer height of about ⅙ of the sphere diameter. The recess 8 is rotationally symmetrical in relation to the piston longitudinal axis 19. In this way, a circularly cylindrical part with a smaller diameter than the sphere diameter is formed between the spherical section 9 and the retaining collar.

The piston 4 has a longitudinal bore 20 (FIG. 5) with 35 an opening at the vertex 13 of the piston head 6, through which the hydraulic pressure from the cylinder chamber is led to the hydrostatic pressure relief face of the surface of the spherical section 9. In order that the pressure can propagate on the pressure relief face a spiral groove 16 is introduced there which originates from the opening of the longitudinal bore in the vertex 13 of the spherical section 9 and ends in a circumferential groove 14 which limits the pressure area. Following the circumferential groove 14 in the form of a circular ring there is formed a sealing surface 15, likewise in the form of a circular ring.

In FIG. 5, the piston 4 and the relationships as the piston 6 is pushed into the spherical shell 5 of the drive flange are illustrated once more in section. The installation is carried out in the mounting direction 17 at the smallest possible angle α between the end face 3 of the drive flange 2 and the piston longitudinal axis 19 so that a sufficiently large difference from the maximum oblique position occurring during the operation of the axial piston machine is provided. The spherical section 9 can be introduced readily into the spherical shell 5 because of the recess 8 while the retaining collar 10 is threaded through the transverse groove described previously. The result is then an operating angle complementary to the angle α of 90° minus a minus a safety margin of at least 10° so that in the working position during the operation of the axial piston machine the piston is retained securely by the spherical shell going beyond the semisphere. 

1. Variable capacity hydrostatic axial piston machine having a drive shaft (1) which has a drive flange (2) having an end face (3) oriented towards displacement pistons (4) in which end face spherical shells (5) for holding substantially spherical piston heads (6) are formed: the calotte of the spherical shells (5) going beyond the semi sphere and each having a circular opening (7) with a smaller diameter than the spherical shell diameter; the spherical calotte of the piston heads (6) having a recess (8) having a smaller diameter than that of the circular opening (7), so that at the vertex (13) of the piston, a spherical section (9) making up less than the semisphere and spaced apart from the latter by the recess (8), a retaining collar (10) having a larger diameter than the circular opening (7) of the spherical shells (5) are formed; and a transverse groove (11) being formed in the circular openings (7) of the spherical shells (5) in such a way that the piston head (6) with the retaining collar (10) can be threaded into the spherical shell (5) through the transverse groove (11) and is retained there in the working position of the piston (4).
 2. Axial piston machine according to claim 1, in which the retaining collar (10) forms a spherical layer which begins approximately in the central plane of the spherical dome of the piston heads (6).
 3. Axial piston machine according to claim 1, in which the retaining collar (10) forms a spherical layer which extends approximately from the central plane of the spherical dome beyond the latter by about ⅛ to ¼, preferably about ⅙ of the sphere diameter.
 4. Axial piston machine according to claim 1, in which the recess (8) is rotationally symmetrical in relation to the piston longitudinal axis (19).
 5. Axial piston machine according to claim 1, in which the transverse grooves (11) of the spherical shells form a circular ring around the axis of the drive shaft (1).
 6. Axial piston machine according to claim 1, in which, in order to thread them into the spherical shells (5) the pistons (6) can be set at an angle (α) to the end face (3) of the drive flange (2) which is smaller than the smallest such angle occurring during the operation of the axial piston pump.
 7. Axial piston machine according to claim 6, in which mounting grooves (12) are provided in the end face (3) of the drive flange (2) which make threading possible at a minimum angle (α) between the piston longitudinal axis (19) and the end face (3) of the drive flange (2).
 8. Axial piston machine according to claim 1, in which the pistons (6) have a bore (20) in the longitudinal direction through which hydraulic pressure is led from the cylinder chamber to the spherical section (9) of the piston head (6) for the purpose of balancing the hydrostatic load on the mounting.
 9. Axial piston machine according to claim 8 in which in order to limit the hydrostatic balancing force a circumferential groove (14) is formed in the spherical section (9) of the piston head (6) and is surrounded on the outside by an annular spherical layer as a sealing surface (15).
 10. Axial piston machine according to claim 9 in which a spiral groove (16) is formed in the spherical section (9) of the piston head (6) from the bore (20) as far as the circumferential groove (14). 